Electrical stress is an undesirable phenomenon that occurs where there is a high electric field in regions at significantly different electric potentials. If not managed or controlled properly, electrical stress can lead to partial discharge, such as in the form of corona discharge, or dielectric breakdown, which causes regions within a dielectric or insulating material to breakdown and not provide the needed insulation properties. Voltage sensors that measure an electric field as a means of determining voltage between a current carrying cable and another potential, such as ground, are placed between conductive structures at the different potentials of interest. To prevent arcing between the current carrying cable and ground, the point of measurement of a high voltage potential can be brought a distance away from the high potential cable along various conductors that can pass through various dielectric structures, including air. The respective rates of expansion and contraction of the conductive and non-conductive structures or mediums are different, which can create a risk of fracture at a conductive-dielectric interface. Areas of high electrical stress are the most vulnerable to these effects. For voltage sensors that measure a voltage between a high voltage potential and ground, examples of such vulnerable areas include where a grounded conductive surface interfaces with a non-grounded conductive surface or where a low dielectric medium or material (e.g., air) abruptly transitions to a high dielectric material or medium.
In addition, to bring a high electric potential to a voltage sensor located a distance away from the current carrying cable, a conductive structure couples the voltage potential from the current carrying cable to an area where the voltage sensor is located. During an extreme electrical fault that exceeds the rated dielectric strength, the conductive structure serves as a low resistance path, allowing the current to create unintended paths by arcing across or through dielectrics or cause thermal breakdown of dielectrics, which can damage the voltage sensor or pose a safety hazard to human operators or other personnel near the conductive structure. The larger the cross sectional area of the conductive structure, the more current it can carry, creating a commensurately greater risk to human safety and equipment integrity.
A need exists for a stress control apparatus that suppresses or eliminates the possibility of partial discharge or dielectric breakdown, safely manages overcurrent conditions or other fault conditions, and avoids other problems to extend the life, accuracy, and integrity of a voltage sensor, and methods of making the same.